Introduction to differential equations as ultimate codes of Nature, just like a seed contains the entire programme of the tree. Linear differential equations with examples of Central Forces - combining the simple harmonic motion, uniform circular motion, projectile motion and planetary motion etc. in scalar and also in vector treatment. Side by side differential equations are learnt. The course covers the curriculums of CBSE, ICSE,and various state councils for +2 level in India and equivalent courses abroad. Elementary processes of indefinite integral, definite integral extensively treated with beta and gamma functions, improper integrals, and applications to calculation of centre of gravity, moment of inertia, transient currents and LCR circuits.Also a preparatory fundamental for IITJEE and other entrance exams. The celebrated coaching institutes expect this fundamental from the students they prepare for exams. But they impart only advanced problems and this book shall fill up the gap.